The Cell Wall of Bacteria

Unlike in plant cells, the cell wall in prokaryotic bacteria is composed of peptidoglycan. This molecule is unique to bacterial cell wall composition. Peptidoglycan is a polymer composed of double-sugars and amino acids (protein subunits). This molecule gives the cell wall rigidity and helps to give bacteria shape. Peptidoglycan molecules form sheets which enclose and protect the bacterial plasma membrane. The cell wall in gram-positive bacteria contains several layers of peptidoglycan. These stacked layers increase the thickness of the cell wall. In gram-negative bacteria, the cell wall is not as thick because it contains a much lower percentage of peptidoglycan. The gram negative bacterial cell wall also contains an outer layer of lipopolysaccharides (LPS). The LPS layer surrounds the peptidoglycan layer and acts as an endotoxin (poison) in pathogenic bacteria (disease causing bacteria). The LPS layer also protects gram-negative bacteria against certain antibiotics, such as penicillins.

Cell Wall Key Points

• The cell wall is an outer protective membrane in many cells, including plants, fungi, algae, and bacteria. Animal cells do not have a cell wall.
• The main functions of the cell wall are to provide structure, support, and protection for the cell.
• The cell wall in plants is composed mainly of cellulose and contains three layers in many plants. The three layers are the middle lamella, primary cell wall, and secondary cell wall.
• Bacterial cell walls are composed of peptidoglycan. Gram-positive bacteria have a thick peptidoglycan layer and gram-negative bacteria have a thin peptidoglycan layer.